I flashed my 3750 to 3450. Then, I flashed region 41 froma real 3490 and it became a 3490. Then I flashed to 3790 US. It worked but the GPS was still a 3490 (which was expected). I tried to flash CHN fw but got rebooting loop. I flashed by original region 41 from a 3750 to try to get back to original.

This was not enough. I dumped all regions and noticed region 34 was altered with a 1101 HWID that appeared in region 34. I flashed both original region 34 & 41 and now I am back to normal as a 3750 that can be flashed to CHN and other foreign firmware.

Conclusion: beware of a few more bytes in region 34. That could be the issue you had to switch to SgMy.

The condition of not rebooting inside this asian firmware is the following:
(region34.hwid == 0x4EB AND region43.hwid == 0x4EB ) OR region34.hwid == 0xFFFF
So it's enough to copy both region34 and region43 from asian device, but you'd better don't do it, because region43 is x-loader, so you can brick your device in the most reliable way
The better solution is to set region34.hwid = 0xFFFF. region34.hwid is placed in two bytes at offset 0x10.
Also turboccc's 3750 works fine because is has region34.hwid == 0xFFFF.

You can find in my previous post, that I have checked this combination, I mean clearing region 34 at offset 0x10, I have put there FF. I will check it again, thanks, but maybe there is something else which prevent my nuvi from running asian firmware?

Which asian firmware did you try? Give me the link.
Maybe there is really something I've missed. I can just upload patched firmware if you want.
Actually my info is valid for TWN firmware. I haven't checked SG-MY. But I'm good at solving reboot problems.

I have gotten then "system software missing". I was able to turn nuvi off, but after start again software missing. I have flashed TW 2.50 for the second time with no change. Now I have returned to EU/US firmware. I have checked tested regions and found no changes.

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